Of course there are aliens out there. I wouldn't count on finding Klingons/Romulans/Vulcans though, there may be other humanoid life, but look how diverse life is just here on earth, there's no telling what's living out there.

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Originally Posted by vortish

just a quick question to those following this thread do you think that if a older civilization is out there do they posses the ability to use warp type propulsion

Yes, just as we one day crossed the oceans, so it can be with the vast distances of space. It's just a technology we don't have yet. Anyway how could they be visiting us now without having developed that technology. Twice in my lifetime I have witnessed something from another world, I have described both incidents before so I won't repeat them now. They were both life changing events that I can never forget, it will be the same for you if you ever see such a thing.

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Originally Posted by ThePhotonist

True a gamma ray laser could work but do we have the capability to generate gamma rays efficiently at that intensity?

Probably not yet, but that is just an engineering detail that can be solved.

Alienlaser, what were the experiences or where will I be able to find them? I am just curious now.

Are you talking to me? Or to Alienlaser? I posted in two threads but I don't remember where, it was a long time ago. If you want I'll explain again what happened both times.

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Originally Posted by LaserTaco

No it belongs in the jokes thread.

I agree.

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Originally Posted by Pi R Squared

Of course there are aliens out there. I wouldn't count on finding Klingons/Romulans/Vulcans though, there may be other humanoid life, but look how diverse life is just here on earth, there's no telling what's living out there.

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Originally Posted by LaserTaco

What if we're the first aliens?

Then it sure took a long time for life to develope. We are the product of a supernova explosion a very long time ago. There should have been civilizations rise and fall in our region of space long before we were here.

The fact of the matter is that yes it is highly probable that there is other lifeforms in the universe. The milky way galaxy is just to big of a place for there not to be other life. The chances of there being other life is just to great. There is something like 100 billion stars in the galaxy and if each one has a planetary system that means out of that 100 billion there has to be at least one other civilization out there

Definitely an issue with lightsails, but laser propulsion could be on a ship just like an EM drive. The reason why it isn't frequently proposed is that the power supply mass wouldn't be worth it with the tiny thrust. The issues are pretty much the same between on board laser propulsion and EM drives. Unless EM drives are hugely propulsive, a nuclear reactor would have to have too little mass.

Edit: A critical exta bit of info on the momentum of light is that it's inversely proportional to the wavelength. X-ray or gamma propulsion might be able to produce more thrust for the same amount of photons. A delicate balance would have to be struck between the mass of the emitter, power requirements, efficiency, and wavelength.

That may be the case - but keep in mind, the energy of a photon is proportional to wavelength - so as the wavelength goes down the energy goes up.

So if you're producing the same number of photons the energy input required to do so increases as the wavelength decreases, thus you'd expect the thrust to increase too, or the efficiency to decrease if thrust remains constant.

There's still much we don't understand about physics, we've come a long way but I don't think we're even anywhere near close to a complete understanding. Every answer seems to bring a new question.

We live at the bottom of a very deep gravity well: the lowest part of the well is the surface of the Earth and its top is interplanetary space. Each kilogram of mass on the Earth's surface has an energy debt of 63 million joules that must be paid to get out of the Earth's well. That in itself isn't so bad; at standard commercial power rates 63 megajoules of electrical energy costs less than $1. But this isn't the true cost. Our gravity well has no bucket, no rope, no crank. The lifting can only be done very inefficiently with expensive, complicated, and not completely reliable chemical rockets. Using that technology it costs between $4,000 and $10,000 per kilogram to ferry payload mass to low earth orbit with the Shuttle.

But there may be another way. Laser powered launching to orbit is an emerging space technology that may eventually provide a techno-fix for the large expense of getting payloads into orbit, a way around the high cost of Shuttle payloads. Extremely powerful lasers are now on the hi-tech horizon, and their development promises to make this new technology feasible. In July of 1986 a group of experts gathered at Lawrence Livermore National Laboratory to consider the key issues of laser propulsion. They focused on three basic questions: (1) What laser launching will be possible with the big lasers now under development? (2) What groundwork of research and development is needed to prepare for launch testing when the big lasers are ready? And (3) What characteristics should be pushed for in these big lasers so that they will be more useful for such launching? This Alternate View column follows some of their discussion.

The idea of laser-powered propulsion is not new. It was first proposed by Arthur Kantrowitz in 1972, but recently it has been given a new twist. The twist, which will be discussed further below, is to eliminate engine hardware altogether from the launch vehicle and to obtain thrust instead from the laser-sustained detonation (LSD) of a thin flat layer of inert fuel that pushes explosively against the vehicle's planar rear surface. This new concept emerged from discussions at the Livermore workshop and seems to offer the long sought inexpensive highway into space, the cheap elevator for lifting payloads from our gravity well.

Until recently there seemed little prospect of developing lasers large enough to launch useful payloads from the ground. However, the DOD's Strategic Defense Initiative Office (SDIO, a.k.a. "star wars") is presently spending quite large amounts of money on the development of gigawatt-level free electron lasers for possible use in the military "defensive shield" that we read about in the newspapers. These powerful lasers, while they may never meet the SDIO goals, appear likely to provide a nearly ideal power source for laser launching. It is somehow ironic that an unplanned spinoff of the big federal investment in SDI may be a cheaper way to put bulk loads and later people into space.

How does laser power propulsion work? Let's start by contrasting it with conventional chemical-fuel propulsion. In conventional rockets the fuel serves two separate and distinct functions: (1) it burns, converting chemical energy to the kinetic energy of the high speed exhaust particles, and (2) the burned fuel supplies the reaction mass of exhaust particles ejected at the exit nozzle. The dual function of the fuel makes any chemical rocket dangerous and expensive because all that stored chemical energy in the fuel is a significant explosion hazard. Rocket design requires careful attention to this problem. The trick in the laser powered launching scheme is to separate the two functions of the fuel: let a ground-based laser supply the propulsion energy, far more energy per fuel mass than chemical burning could supply, while a safe chemically inert "fuel block" supplies the reaction mass. Kantrowitz (now on the Dartmouth University faculty) and Dr. Jordin Kare, the Livermore workshop coordinator, describe this latest laser powered launch scheme as the "4-P" launch technology. It leaves everything on the ground except "Payload, Propellant, and Photons ... Period!"

How might such a "4-P" vehicle operate? Imagine the launch vehicle as a pyramid about 200 cm high (about the size a pyramid camping tent) made of solid material with about the density of water. The top 91 cm of the pyramid (mass about 1 metric ton) is the payload. The bottom 109 cm (mass about 9.7 tons) is the expendable "fuel block" to be consumed during the launch. This vehicle would probably receive its initial velocity from a Jules-Verne-style launch cannon which accelerates at 10 g's and fires vertically. After the vehicle leaves the cannon it is tracked by the intense beam of the free electron laser, which begins detonating fuel on the backside of the vehicle to propel it into orbit. The laser, probably delivering average power of 100-1000 megawatts, provides the propulsion energy while the fuel block provides the reaction mass.

The laser must be pulsed in a carefully programmed way. A relatively low energy "metering pulse" from the laser vaporizes a thin layer of fuel from the flat rear surface of the fuel block. The gas thereby produced drifts away from the rear surface of the vehicle. Then, when the dispersing gas reaches the proper density, the laser hits again with a far more powerful pulse, converting the vaporized fuel to a very hot plasma of dissociated electrons and ionized atoms. This plasma absorbs energy rapidly and detonates explosively. The shock wave from the LSD wave provides the push. This is the pulsed LSD propulsion scheme mentioned above. It's a revolutionary concept in rocketry. There are no on-board engines, no plumbing, no pumps, no valves, no potentially explosive fuel, no nozzles, no coolants, no stage-separation explosives, no solid-fuel boosters, no O-rings, ...

In a normal rocket engine the explosion of burned fuel is roughly spherical and continuous, so that carefully cooled engine walls and nozzles must convert the omnidirectional pressure of the exploding fuel into directed thrust. But the LSD explosion comes in a pulse and has the geometry of a plane, not a sphere. The exploding gas does not have to be redirected. Half of the gas molecules will push against the surface of the fuel block, providing thrust, and the other half of the molecules will dissipate in the opposite direction. Only at the edges of the plane LSD wave is there deviation from the plane geometry of the explosion, and this has negligible effects. The LSD wave propulsion scheme is a chamber-less nozzle-less engine-less engine.

It is worth noting that the SDI people have some very severe problems to overcome is making their energetic lasers destroy missiles. It is difficult to make free electron lasers operate at the near-infrared wavelengths that SDI needs. But laser powered propulsion works quite well at more accessible far-infrared wavelengths. Another problem for SDI involves the LSD waves themselves: if the target missile has a simple vaporizable coating the laser beam's energy may be dissipated in heating the vaporized coating rather than destroying the missile. But for laser powered launching the shielding effect of the plasma is a benefit because it insures that the laser energy is absorbed by the vaporized fuel rather than the payload or the solid fuel block.

What are the problems with the scheme? The biggest one, of course, is getting that big laser to use. Free electron laser technology will be discussed a bit later. A second problem is finding a suitable fuel block material that will operate efficiently and that will not be eroded too rapidly. Ice, plastic, and lithium metal have been discussed, but more research is needed. The structural and hydrodynamic effects of the detonation waves must be understood. And of course the aerodynamics of the vehicle will have to be carefully considered. It will require attitude-control hardware, vanes or jets perhaps, to keep it oriented properly in the beam. The laser tracking to orbit will also require careful design. When the vehicle had reached some altitude and velocity, it must be turned so that the back surface of the fuel block is at an angle to the incoming laser beam. This allows the proper tangential velocity to be added to achieve a stable orbit. Notice that the thrust in the tilted configuration remains at right angles to the block surface and is quite independent of the laser beam angle. If this technology is to become widespread, the environmental effects of noise pollution from the launch site, the atmospheric effects of the laser beam (e.g., nitrous oxide generation), interference with air traffic, etc., must also be carefully studied. But at present the biggest problem is to find a funding agency that will pay for this research. Unfortunately NASA is reportedly not interested.

Let's now turn to the technology of the free electron laser (FEL). It's a spinoff, just 10 years old, of accelerator technology developed for nuclear physics basic research in the past few decades. Basically an FEL is a large electron linear accelerator that accelerates perhaps 10 amperes of electrons to nearly the speed of light, giving them energies around 100 million electron volts. At such energies an electron weighs about 200 times more than it would at rest due to relativistic mass increase. The acceleration of the electrons may either be continuous, using resonant electrical cavities powered by high frequency electrical power, or it may be pulsed with a set of microwave "transformers" that use the electron beam as the effective secondary winding. The latter acceleration scheme appears to be the more useful for LSD wave propulsion, which requires a pulsed laser beam in any case.

After acceleration the electron beam passes into a "wiggler", an intense and rapidly alternating set of static magnetic fields. The wiggler efficiently converts the energy contained in the electron beam to coherent photons and a few hundred megawatts of coherent light energy emerges from the machine. The FEL's conversion of electrical energy to light energy is remarkably efficient. Overall efficiencies of 20% or more have already been achieved with low power FEL devices. A low power FEL was first demonstrated at Stanford University a decade ago, but until the SDIO made FEL development a national priority, it progressed rather slowly. But now with SDI funds as the driving force, two national laboratories and several aerospace companies are in a development horse race. A major facility to test high power FEL devices is being constructed at White Sands Proving Grounds in New Mexico. It's curious to consider that that site, where captured V-2 rockets were tested after WWII, may eventually become our first laser spaceport.

This brings us to bottom line: the cost of putting a kilogram of mass in low earth orbit with the laser power launch scheme. It's estimated that it will cost a billion dollars or so to produce a FEL installation powerful enough for laser launching. If that cost must be amortized as part of the launch cost, that cost at 10% of maximum capacity is about $180 per kilogram. At 100% utilization the cost drops to $30 per kilogram. If one uses a laser "built for other purposes" such as SDI and does not have to amortize the capital cost, the minimum cost drops to $18 per kilogram. Compared to the $4000 to $10,000 per kilogram cost of Shuttle freight, laser launching looks very attractive indeed.

Gamma emission is hard for us to produce without radioactive decay, but there's been research going into finding gamma fluorescent materials for medical imaging.

Quote:

Originally Posted by diachi

That may be the case - but keep in mind, the energy of a photon is proportional to wavelength - so as the wavelength goes down the energy goes up.

So if you're producing the same number of photons the energy input required to do so increases as the wavelength decreases, thus you'd expect the thrust to increase too, or the efficiency to decrease if thrust remains constant.

There's still much we don't understand about physics, we've come a long way but I don't think we're even anywhere near close to a complete understanding. Every answer seems to bring a new question.

As for IE's joke post - nothing wrong with some humor!

Yep. I probably should have explained more. The energy is directly proportional to the momentum of light. 10W of any wavelength will produce the exact same amount of force. Some labs measure laser power this way, and it's much more effective.

The critical bit is that the processes to produce photons at different wavelengths are very different, so finding the balance is the crucial part.

Where you could really see a difference with very high wavelengths is in the emitter size (and hopefully weight). A mole of atoms emitting gamma rays will produce a huge amount of thrust compared to a mole of atoms emitting anything else. The technology has to be developed to determine how much power density you could get out of a gamma emitter.

"Open your eyes, lookwithin. Are you satisfied with the life you're living?" -Bob Marley “The universe is a pretty big place. If it's just us, seems like an awful waste of space.” -Carl SaganYou are important: Pale Blue Dot